Radiation based patterning methods

ABSTRACT

Stabilized precursor solutions can be used to form radiation inorganic coating materials. The precursor solutions generally comprise metal suboxide cations, peroxide-based ligands and polyatomic anions. Design of the precursor solutions can be performed to achieve a high level of stability of the precursor solutions. The resulting coating materials can be designed for patterning with a selected radiation, such as ultraviolet light, x-ray radiation or electron beam radiation. The radiation patterned coating material can have a high contrast with respect to material properties, such that development of a latent image can be successful to form lines with very low line-width roughness and adjacent structures with a very small pitch.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of copending U.S. patent applicationSer. No. 16/885,581 to Stowers et al., filed on May 28, 2020, entitled“Radiation Based Patterning Methods,” which is a continuation of U.S.patent application Ser. No. 15/784,258 to Stowers et al. (now U.S. Pat.No. 10,782,610), filed on Oct. 16, 2017, entitled “Radiation BasedPatterning Methods,” which is a divisional of U.S. patent applicationSer. No. 14/858,612 to Stowers et al. (now U.S. Pat. No. 9,823,654),filed on Sep. 18, 2015, entitled “Patterned Inorganic Layers, RadiationBased Patterning Compositions and Corresponding Methods,” which is acontinuation of U.S. patent application Ser. No. 12/850,867 to Stowerset al. (now U.S. Pat. No. 9,176,377), filed Aug. 5, 2010, entitled“Patterned Inorganic Layers, Radiation Based Patterning Compositions andCorresponding Methods,” which claims priority to U.S. provisional patentapplication No. 61/350,103 to Stowers et al., entitled “PhotopatternableInorganic Hardmask,” all of which are incorporated herein by reference.

STATEMENT AS TO GOVERNMENT RIGHTS

Development of the inventions described herein was at least partiallyfunded with government support through U.S. National Science Foundationgrants DGE-0549503 and IIP-0912921, and the U.S. government has certainrights in the inventions.

FIELD OF THE INVENTION

The invention relates to patterned inorganic layers that can be used toform elements of devices and/or as a resist for facilitating thepatterning of other materials. The invention further relates toradiation based methods for the performance of the patterning and toprecursor solutions that can be deposited to form a coating that can bepatterned with very high resolution with radiation.

BACKGROUND OF THE INVENTION

For the formation of semiconductor-based devices as well as otherelectronic devices, the materials are generally patterned to integratethe structure. Thus, the structures are generally formed through aniterative process of sequential deposition and etching steps throughwhich a pattern is formed of the various materials. In this way, a largenumber of devices can be formed into a small area. Some advances in theart can involve that reduction of the footprint for devices, which canbe desirable to enhance performance.

Organic compositions can be used as radiation patterned resists so thata radiation pattern is used to alter the chemical structure of theorganic compositions corresponding with the pattern. For example,processes for the patterning of semiconductor wafers can entaillithographic transfer of a desired image from a thin film of organicradiation-sensitive material. The patterning of the resist generallyinvolves several steps including exposing the resist to a selectedenergy source, such as through a mask, to record a latent image and thendeveloping and removing selected regions of the resist. For apositive-tone resist, the exposed regions are transformed to make suchregions selectively removable, while for negative-tone resist, theunexposed regions are more readily removable.

Generally, the pattern can be developed with radiation, a reactive gasor liquid solution to remove the selectively sensitive portion of theresist while the other portions of the resist act as a protective etchresistant layer. However, liquid developers can be used effectively todevelop the image. The substrate can be selectively etched through thewindows or gaps in the remaining areas of the protective resist layer.Alternatively, desired materials can be deposited into the exposedregions of the underlying substrate through the developed windows orgaps in the remaining areas of the protective resist layer. Ultimately,the protective resist layer is removed. The process can be repeated toform additional layers of patterned material. The functional inorganicmaterials can be deposited using chemical vapor deposition, physicalvapor deposition or other desired approaches. Additional processingsteps can be used, such as the deposition of conductive materials orimplantation of dopants. In the fields of micro- and nanofabrication,feature sizes in integrated circuits have become very small to achievehigh-integration densities and improve circuit function.

SUMMARY OF THE INVENTION

In a first aspect, the invention pertains to an aqueous inorganicpatterning precursor solution comprising a mixture of water, metalsuboxide cations, polyatomic inorganic anions and ligands comprisingperoxide groups, wherein the composition has a molar concentration ratioof ligands to metal suboxide cations of at least about 2 and wherein theresist composition is stable with respect to phase separation for atleast about 2 hours without additional mixing.

In a further aspect, the invention pertains to a method for formation ofa radiation sensitive inorganic coating precursor solution, the methodcomprising combining a first aqueous solution comprising metal suboxidecations, a complexing solution comprising a ligand having a peroxidegroup and a composition comprising a polyatomic inorganic anion to formthe coating precursor solution. In some embodiments, the molarconcentration ratio of ligands to metal suboxide cations is at leastabout 2.

In another aspect, the invention pertains to a method for patterning aninorganic material on a substrate, the method comprising forming a layerof a radiation patternable coating material to form a coated substrate,heating the coated substrate to remove at least a portion of thesolvent, exposing the coated substrate to a pattern of radiation andheating the coated substrate after irradiation. Generally, the patternedcoating material comprises metal suboxide cations, ligands comprising aperoxide group and inorganic polyatomic anions. The irradiation of thecoated substrate can condense the coating at the irradiated locations.The heating of the coated substrate after irradiation can be to atemperature of at least about 45° C. prior to contacting the coatingwith a developer.

In other aspects, the invention pertains to a patterned structurecomprising a substrate and a patterned inorganic material on a surfaceof the substrate. The patterned inorganic material can comprise apatterned semiconductor material or a patterned dielectric material, andthe patterned inorganic material can have edges with an averageline-width roughness no more than about 2.25 nm at a pitch of no morethan about 60 nm or for individual features having an average width ofno more than about 30 nm.

In additional aspects, the invention pertains to a method for forming apatterned structure comprising a substrate and a patterned inorganicmaterial on a surface of the substrate. The method can compriseirradiating a layer of coating material with extreme ultraviolet lightat a dose of no more than about 100 mJ/cm² or an electron beam at a doseequivalent to no more than about 300 C/cm² at 30 kV, and contacting theirradiated layer with a developing composition to dissolve un-irradiatedmaterial to form the patterned inorganic material. In some embodiments,the patterned inorganic material has an average pitch of no more thanabout 60 nm or for individual features having an average width of nomore than about 30 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing depicting a metal cation bonded to aligand, where M represents a metal atom and O represents an oxygen atom,undergoing a condensation reaction triggered by energy absorption fromradiation.

FIG. 2 is a schematic perspective view of a radiation patternedstructure with a latent image.

FIG. 3 is a side plan view of the structure of FIG. 2.

FIG. 4 is a schematic perspective view of the structure of FIG. 2 afterdevelopment of the latent image to remove un-irradiated coating materialto form a patterned structure.

FIG. 5 is a side view of the patterned structure of FIG. 4.

FIG. 6 is a side plan view of the patterned structure of FIGS. 4 and 5following etching of the underlayer.

FIG. 7 is a side plan view of the structure of FIG. 6 following etchingto remove the patterned, condensed coating material.

FIG. 8 is a side plan view of a “thermal freeze” double patterningprocess flow. The process shown in FIGS. 2-4 is repeated after a bakethat renders the first layer insoluble to the second layer.

FIG. 9 is a scanning electron micrograph of step coverage over a metalgate line with a step of about 100 nm in height with Hf-based coatingmaterial.

FIG. 10 is a scanning electron micrograph of 120-nm pitch lines inZr-based coating material patterned via 193-nm wavelength interferencelithography at a dose level of 20 mJ/cm².

FIG. 11 is a scanning electron micrograph of 36-nm pitch lines inHf-based coating material patterned via electron-beam lithography.

FIG. 12 is an expanded view of a portion of the pattern shown in FIG.11.

FIG. 13A is a scanning electron micrograph of 36 nm pitch postspatterned by e-beam developed in 2.38% TMAH.

FIG. 13B is a scanning electron micrograph of 36 nm pitch postspatterned by e-beam developed in 25% TMAH.

FIG. 14 is a scanning electron micrograph of a portion of a developedpattern having a line with roughness from 1.6-1.8 nm.

FIG. 15 is a scanning electron micrograph of a double patternedstructure formed using e-beam lithography with a coating material asdescribed herein.

FIG. 16 is an expanded view of a portion of the pattern shown in FIG.15.

FIG. 17 is a scanning electron micrograph of etched silicon nanopillarsof width 40 nm. The pillars were fabricated via ion-etching through ahard mask formed with a Hf-based coating material.

FIGS. 18A-D are scanning electron micrographs of EUV lithographyperformed with the Hf-based coating materials described herein anddeveloped in 25% TMAH. In each case, the figure shows lines and spacesof a given pitch, comprised of lines with widths approximately half thestated pitch: 18A) 32-nm pitch lines and spaces, 18B) 30-nm pitch linesand spaces, 18C) 28-nm pitch lines and spaces, 18D) 26-nm pitch linesand spaces.

DETAILED DESCRIPTION OF THE INVENTION

Significant improvements in inorganic precursor solutions provide forsuperior direct patterning results for inorganic oxide materialscomprising polyatomic ions. The precursor solutions can be used todeposit an inorganic coating material that is radiation sensitive. Inembodiments of particular interest, exposure to the radiation convertsthe irradiated coating material into a condensed material that isresistant to removal with a developer composition. Selective removal ofat least a portion of the un-irradiated coating material leaves apattern including regions of the condensed coating material and regionswhere the un-irradiated coating material has been removed to expose theunderlying substrate. The coating materials can be designed to besensitive to selected radiation, such as ultraviolet light and/orelectron beams. Furthermore, the precursor solutions can be formulatedto be stable with an appropriate shelf life for commercial distribution.

The compositional changes to form the improved precursor solutions alsoprovide for improved development of the image. In particular, theirradiated coating material can result in a stable inorganic materialwith a high level of resistance to the developer, e.g., a suitableliquid to dissolve un-irradiated coating material. Thus, the coatinglayers can be made thin without removing the condensed coating materialduring development. Compared to conventional organic resists, theinorganic materials described herein have extremely high resistance tomany etch chemistries for commercially relevant functional layers. Thisenables process simplification through avoidance of intermediatesacrificial inorganic pattern transfer layers that would otherwise beused to supplement the patterned organic resists with respect to themask function. Also, the coating material provides for convenient doublepatterning. Specifically, following a thermal treatment, condensedportions of the coating material that have been irradiated are stablewith respect to contact with many composition including furtherprecursor solutions. Thus, multiple patterning can be performed withoutremoving previously deposited hard-mask coating materials.

The patterned inorganic coating material can be subsequently removedafter the patterned material is used as a mask to pattern desiredfunctional materials. Alternatively, the resulting patterned inorganicmaterial can be incorporated into the structure as a component of thedevice(s). If the patterned inorganic coating material is incorporatedinto the structure, many steps of the processing procedure can beeliminated through the use of a direct patterning of the material withradiation. Alternatively, it has been found that very high resolutionstructures can be formed using thin inorganic coating materials exposedusing short wavelength electromagnetic radiation and/or electron beams,and that line-width roughness can be reduced to very low levels for theformation of improved patterned structures.

The formation of integrated electronic devices and the like involves thepatterning of the materials to form individual elements or componentswithin the structures. Generally, this patterning involves differentcompositions covering portions of layers that interface with each otherto induce desired functionality. The various materials can comprisesemiconductors, which can have selected dopants, dielectrics, electricalconductors and/or other types of materials. To form high resolutionpatterns, radiation sensitive organic compositions can be used tointroduce patterns, and the compositions can be referred to as resistssince portions of the composition are processed to be resistant todevelopment/etching such that selective material removal can be used tointroduce a selected pattern. Radiation with the selected pattern or thenegative of the pattern can be used to expose the resist and to form apattern or latent image with developer resistant regions and developerdissolvable regions. The radiation sensitive inorganic compositionsdescribed herein can be used for the direct formation of desiredinorganic material structures within the device and/or as a radiationpatternable inorganic resist that is a replacement for an organicresist. In either case, significant processing improvements can beexploited, and the structure of the patterned material can be alsoimproved.

To form the coating material, a precursor solution is applied to asurface of a substrate, such as a wafer or the like. In someembodiments, the inorganic precursor solution can have a relatively lowconcentration of metal ions such that the rheology of the coatingcomposition, e.g., the viscosity, allows the formation of a thin coatingon the substrate. The use of a thinner coating is consistent with theformation of higher resolution structures upon exposure to radiation anddevelopment of the pattern. The relatively high density and smallspatial dimensions of the independently processable chemical moieties ofthe coating material can be exploited for the formation of structureswith reduced line-width roughness, small feature sizes and/or extremelyhigh resolution.

The coating materials described herein can be designed for use withparticular radiation types, and the precursor solution can becorrespondingly formulated to provide the desired coating materialcomposition. In particular, the coating materials can be engineered tohave a desired absorption of a selected radiation, and use of a coatingmaterial with a greater absorption cross section of the radiation allowsfor the corresponding use of a lower radiation dose. With appropriateselection of the composition, the patterning composition can besensitive to, for example, ultraviolet light, x-rays or electron beams,as well as a particular wavelength or range of wavelengths within eachradiation type. These particular radiation types are desirable due tothe ability to form small patterns based on short radiation wavelengths.Thus, using the coating materials described herein, small patterns canbe effectively formed with corresponding low line-width roughness thatcan enhance device formation abilities. Also, since the radiationpatterned coating material is thin and has a high contrast with respectto sensitivity to appropriate developers, following removal of theun-irradiated coating material, the structures can have a small pitchbetween adjacent structures.

The precursor solution comprises an aqueous solution with metal suboxidecations, radiation sensitive ligands comprising peroxide groups, andpolyatomic anions. Metal suboxide cations are polyatomic cations with ametal element and covalently bonded oxygen atoms. Aqueous solutions ofmetal suboxide or metal hydroxides can tend to be unstable with respectto gelling and/or precipitation. In particular, the solutions areunstable upon solvent removal and can form oxo-hydroxide networks withthe metal cations. The precipitated materials though can have usefulproperties, as described below. The precursor solutions have beenformulated with improved stability and control of the precipitation sothat radiation can be used to induce a change in the material. Inparticular, peroxide-based ligands stabilize the precursor solutionswhile also providing control over the processing of the materials.

Specifically, the precursor solution can comprise sufficient radiationsensitive ligands such that the solution has a molar concentration ratioof radiation sensitive ligands to metal suboxide cations of at leastabout 2 and in some embodiments at least about 5. In particular, thehigher peroxide-based ligand concentrations provide for a surprisinglylarge improvement in the precursor stability. While not wanting to belimited by theory, the increase in the radiation sensitive ligandconcentration evidently reduces agglomeration of the metal cations tostabilize the solution. Thus, the precursor solution can be stablerelative to settling of solids without further stirring for at least twohours and possibly for significantly longer periods of time, such asgreater than a month. Due to the long stability times, the improvedprecursors have increased versatility with respect to potentialcommercial uses. Hydrogen peroxide provides a desirable radiationsensitive ligand, although other inorganic peroxides can be suitable. Insome embodiments, an organic peroxide can be used, but generally theorganic components should be removed thoroughly for the formation of thefinal product at least for some electronics applications.

Furthermore, it has been discovered that materials formed with metalsuboxide cations and polyatomic anions can provide useful materialproperties, which make the materials suitable for components ofelectronic devices and the like. Additional metal cations and anions canbe incorporated into the materials to adjust the properties. Thesegeneral precursor solutions are described further in published PCTapplication WO 2009/120169 to Keszler et al., entitled “SolutionProcessed Thin Films and Laminates, Devices Comprising Such Thin Filmsand Laminates and Methods for the Use and Manufacture,” incorporatedherein by reference (hereinafter “Keszler PCT application”). Asdescribed herein, significant improvements in the precursor solutionshave been accomplished through the use of significantly higher radiationsensitive ligand concentrations. Even more surprisingly, significantlyincreasing the radiation sensitive ligand concentration in the precursorsolutions results in a coating material that has greater contrastfollowing radiation exposure so that there are surprising added benefitswhere precursor solution stabilization further accomplishes improvedpatterning and shorter development times.

The metal suboxide cations can be selected to achieve the desiredradiation absorption. In particular, ZrO⁺² based coating materialsexhibit good absorption of far ultraviolet light at a 193 nm wavelength.HfO⁺² based coating materials exhibit good absorption of x-ray radiationand electron beam radiation and can also contribute desirable propertiesto the coating material, such as density and smoothness. Some precursorsolutions effectively incorporate a blend of ZrO⁺² and HfO⁺² cations toprovide for desirable overall properties of the coating materials. Theprecursor solutions can comprise additional metal cations to increasethe absorption of some radiation wavelengths of significance forlithography. The metal cations can have various degrees of hydrolysisfrom interactions with water, and the state of hydrolysis with watergenerally is significantly pH dependent. The metal ion concentration canbe selected to provide desired properties for the precursor solution,with more dilute solutions generally consistent with the formation ofthinner coating materials.

Sulfate anions can be desirable polyatomic anions for incorporation inthe precursor solutions, although other polyatomic anions can bedesirable alternatives or additions to the sulfate anions. Theconcentration of polyatomic anions has been found to correlate with thesensitivity of the coating material to various developer compositions.Some polyatomic anions comprise metal atoms with covalent bonds withoxygen atoms and/or hydroxide groups, and anion structure can also be pHdependent.

Refined precursor solutions with greater stability also provide for acoating material having the potential of a greater contrast between theradiation exposed and unexposed portions of the substrate. Specifically,the un-irradiated coating material can be relatively more easilydissolved by suitable developer compositions while the exposed coatingmaterial can remain appropriately resistant to the developercomposition. Since the un-irradiated coating material can be relativelymore easily dissolvable with a developer in comparison with theirradiated coating material, the contact time with the developer can bereduced while still maintaining desired removal of the coatingcomposition. Specifically, with the improved compositions andcorresponding materials, line-width roughness has been reduced tosurprisingly low levels. Correspondingly, the pitch can be made verysmall between adjacent elements with appropriate isolation, generallyelectrical isolation, between the adjacent elements. The irradiatedcoating composition can be very resistant to the development/etchingprocess so that the coating composition can be made very thin withoutcompromising the efficacy of the development process with respect toclean removal of the un-irradiated coating composition while leavingappropriate portions of the irradiated patterning composition on thesurface of the substrate. The ability to shorten the exposure time tothe developer further is consistent with the use of thin coatingswithout damaging the exposed portions of the coating.

To perform the patterning, the precursor solution is generally appliedto the entire surface of the substrate or a selected portion thereof.The precursor composition can be deposited onto a substrate, forexample, using conventional coating approaches. Prior to the applicationof the coating material, the substrate surface can be prepared using ahydrophilic surface treatment to increase the hydrophilic nature of thesurface for improved wetting with the aqueous precursor solution. Forexample, precursor solutions can be coated onto wafers or othersubstrates using spin coating, although other coating approaches can beused, such as spray coating, knife edge coating or other appropriatetechniques. Printing techniques, such as screen printing, inkjetprinting and the like, can be used for applying the precursor solution.However, the fine patterning generally is performed with radiation basedpatterning rather than using printing. The removal of at least a portionof the solvent can stabilize the coating material for furtherprocessing. Solvent can be removed in part during the coating processitself. Also, the substrate with the coating material can be heated tocontribute to the removal of solvent. Following the removal ofsufficient solvent, the coating material is generally relatively stableto allow for the patterning and can be further processed for patterning.

The coating material generally is radiation sensitive such that exposureto radiation modifies the composition of the coating material atirradiated regions as a latent image. The radiation pattern can beintroduced through the passage or reflection of the radiation through aphysical mask and suitable optics can be used to deliver the patternedradiation to the coating material. Additionally or alternatively, a beamof radiation can be scanned across the coating material to form apattern in the coating material as a latent image based on exposure tothe radiation. The radiation absorption results in the condensation ofthe irradiated portion of the coating material. In other words, theenergy from radiation absorption results in agglomeration of the metalions to change the character of the irradiated material.

While not wanting to be limited by theory, it is believed that uponabsorption of the radiation, the peroxide functional groups arefragmented, and the composition correspondingly condenses through theformation of bridging metal-oxygen bonds. Through the condensationreaction, the radiation pattern is transferred to a pattern in thecoating material. Specifically, there is a pattern of irradiated, andcorrespondingly condensed, coating material and of un-irradiated coatingmaterial, which is substantially unchanged from its composition prior topatterned irradiation of the coating material.

It has been discovered that the contrast in material properties can beincreased between the condensed coating composition and theun-irradiated coating composition through the heating of the materialfollowing irradiation. In particular, the heating process is found toincrease the condensation of the irradiated coating composition. Theheating does not significantly change the ability to remove theun-irradiated material in a development step.

The patterned coating composition can be exposed to a developer liquid,such as 2.38 weight percent tetramethyl ammonium hydroxide (the standarddeveloper in semiconductor lithography), that removes the un-irradiatedportion of the coating material. The development can be performed in ashort period of time based on the appropriate selection of the developercomposition. Furthermore, due to the stabilization of the condensed,irradiated coating material, the condensed coating material can be verystable against the developer. The condensed coating material forms avery hard masking material.

Following the patterning of the coating material, additional layers ofmaterial can be applied over the pattern and/or additional etching canbe performed through the windows created by removing un-irradiatedcoating material to selectively remove substrate material based on thelatent image in the patterned coating material. In this way, thepatterned coating material can be used to assemble a structure withfurther complementary patterning of various compositions. Ions may alsobe selectively implanted into the substrate through the windows of thepatterned coating material for control of electrical properties. Thedense nature of the patterned inorganic coating provides a higherimplantation resistance relative to a conventional organic patternedcoating. Since the patterned coating material is itself an inorganicmaterial that can incorporate desirable properties to a structure, thepatterned coating material can be directly incorporated into a device.For embodiments in which the coating material is incorporated directlyinto the structure, distinct steps that just accomplish the patterningand removal of a resist are avoided such that very significantprocessing advantages can be achieved. These uses are elaborated on inthe following discussion.

As noted above, the radiation sensitive coating materials describedherein can be used as a negative resist. After developing the patternedcoating material to remove the un-irradiated coating material, thepattern can be used for additional processing steps. In particular, thesubstrate may be etched through the gaps in the patterned coating.Furthermore, additional materials can be deposited with the additionalmaterials penetrating through the gaps in the patterned coating materialto reach the underlying substrate. In some embodiments, combinations ofetching and/or deposition can be based on the pattern in the coatingmaterial. After the additional processing is performed based on thepatterned coating material, the inorganic coating material, i.e.,inorganic resist, can be removed using a suitable etching composition orother etching process. For example, the irradiated coating material canbe removed with a dry BCl₃ plasma etch or an aqueous HF wet etch. Theuse of similar compositions as a negative resist as well as someembodiments of a positive resist is described in the Keszler PCTapplication, which has been incorporated herein by reference. Relativeto organic resists, the inorganic coating material provides distinctadvantages with respect to absorption of selected radiation as well ashigh contrast between exposed and non-exposed regions such that highresolution can be achieved with moderate radiation doses.

The direct use of a patterned radiation-sensitive inorganic coatingmaterial provides the ability to form a patterned inorganic layerwithout the separate use of an organic resist. The large contrast inproperties between the irradiated and non-irradiated regions of theinorganic coating material provides for the ability to form thinpatterned layers in which the non-irradiated portion can be cleanlyremoved without significantly damaging the resistant condensed portionsof the coating material during the development process. Due to thedensity and general etch resistance of the patterned inorganic coatingmaterial, the thin patterned coating material can be effectively usedfor further processing of the structure including, for example, etchingand ion implantation, that is guided by the patterned inorganic coatingmaterial as a mask. In some embodiments, the condensed inorganic coatingmaterial can be designed with an appropriate thickness and physicalproperties to be directly incorporated into the device as a functionalelement. For example, the product metal suboxide compositions can beused as dielectrics, as described in published U.S. patent application2005/0242330A to Herman et al., entitled “Dielectric Material,”incorporated herein by reference. Also, some embodiments of the metalsuboxide compositions exhibit semiconducting properties as described inpublished U.S. patent application 2010/0044698A to Herman et al.,entitled “Semiconductor Film Composition,” incorporated herein byreference. Thus, the coating materials can be selected to haveappropriate functionality.

The general uses of lithographic procedures are well known in theelectronics art. See, for example, U.S. Pat. No. 7,208,341 to Lee etal., entitled “Method for Manufacturing Printed Circuit Board,” Harry J.Levinson, “Principles of Lithography,” 2nd Edition, SPIE Press,Monograph Vol. PM146 (2005), and Chris Mack, “Fundamental Principles ofOptical Lithography, The Science of Microfabrication,”Willey-Interscience (2007), all three of which are incorporated hereinby reference. Generally, the substrate is a single crystal siliconwafer, which may include other layers, although other substrates, suchas polymers, can be used. In particular, the processing temperatures forthe inorganic coating materials described herein are relatively low, sothat the formation of patterned inorganic materials as described hereincan be performed with very high resolution on substrates that may not beable to be processed without damage at higher temperatures, such asabove 600° C. Suitable devices in which elements can be patterned usingthe inorganic coating materials described herein include, for example,integrated electronic circuits, solar cells, electronic displays and thelike.

Precursor Solutions

The precursor solutions have been formulated to achieve very high levelsof stability such that the precursor solutions have appropriate shelflives for commercial products. Also, it has been discovered that theformulation of the precursor solutions can be designed to achievedesired levels of radiation absorption for a selected radiation based onthe selection of the metal cations. The precursor solutions are based onmetal oxide chemistry and aqueous solutions of metal cations withpolyatomic anions. The precursor solutions are designed to form acoating composition upon at least partial solvent removal and ultimatelyan inorganic solid with metal oxides and polyatomic anions. The controlof the precursor solution is based on high concentrations of radiationsensitive ligands to the metal cations, specifically peroxide-basedligands. In particular, if the mole ratio of peroxide groups to themetal cations is at least 2, more stable solutions can be formed. Themore stable precursor solutions provide an added advantage of greatercontrast between the ultimate irradiated coating material andun-irradiated coating material.

The aqueous precursor solutions generally comprise one or more metalcations. In aqueous solutions, metal cations are hydrated due tointeractions with the water molecules. The nature of the interactions isgenerally pH dependent. Specifically, hydrolysis can take place to bondoxygen atoms to the metal ion to form hydroxide ligands or oxo bondswith the corresponding release of hydrogen ions. As additionalhydrolysis takes place, the solutions can become unstable with respectto precipitation of the metal oxide or with respect to gelation.Ultimately, it is desirable to form the oxide material, but thisprogression to the oxide is controlled as part of the procedure forprocessing the solution first to a coating material and then to theultimate metal oxide composition with polyatomic anions. Solvent removalcan contribute to the formation of the oxide, but this approach does notprovide significant control of the process without the use of theperoxide-based ligands as described herein. As described below,peroxide-based ligands can be used to provide significant control to theprocessing of the solution.

Thus, the aqueous solutions of the metal cations are poised for furtherprocessing. In particular, it can be desirous to use as an addedcomponent of the precursor solution, a metal suboxide cation that canpoise the solution further toward a metal oxide composition. In general,the precursor solution comprises from about 0.01M to about 1.4M metalsuboxide cation, in further embodiments from about 0.05M to about 1.2M,and in additional embodiments from about 0.1M to about 1.0M. A person ofordinary skill in the art will recognize that additional ranges of metalsuboxide cations within the explicit ranges above are contemplated andare within the present disclosure. The metal suboxides can be added assuitable salts, such as halides salts, e.g., chlorides, fluorides,bromides, iodides or combinations thereof. Based on the use of the metalsuboxide ions in the precursor solutions, relatively low levels ofheating can be used to form the oxides while maintaining good control ofthe solutions based on the use of the radiation sensitive ligands.

Various metal ions can be provided as metal suboxide cations, such asVO⁺², SbO⁺, ReO₃ ⁺, TiO⁺², TaO⁺³, TaO²⁺, YO⁺, NbO⁺², MoO⁺², WO⁺⁴, WO₂⁺², AlO⁺, GaO⁺, CrO⁺, FeO⁺, BiO⁺, LaO⁺, CeO⁺, PrO⁺, NdO⁺, PmO⁺, SmO⁺,EuO⁺, GdO⁺, TbO⁺, DyO⁺, HoO⁺, ErO⁺, TmO⁺, YbO⁺, LuO⁺, TiO_(y)(OH)_(z)^((4-2y-z)+), TaO_(y)(OH)_(z) ^((5-2y-z)+), YO_(y)(OH)_(z) ^((3-2y-z)+),NbO_(y)(OH)_(z) ^((4-2y-z)+), MoO_(y)(OH)_(z) ^((4-2y-z)+),WO_(y)(OH)_(z) ^((6-2y-z)+), AlO_(y)(OH)_(z) ^((3-2y-z)+,)GaO_(y)(OH)_(z) ^((3-2y-z)+), Zn(OH)⁺, CrO_(y)(OH)_(z) ^((3-2y-z)+),FeO_(y)(OH)_(z) ^((3-2y-z)+), BiO_(y)(OH)_(z) ^((3-2y-z)+),LaO_(y)(OH)_(z) ^((32y-z)+), CeO_(y)(OH)_(z) ^((3-2y-z)+),PrO_(y)(OH)_(z) ^((3-2y-z)+), NbO_(y)(OH)_(z) ^((3-2y-z)+),PmO_(y)(OH)_(z) ^((3-2y-z)+), SmO_(y)(OH)_(z) ^((3-2y-z)+),EuO_(y)(OH)_(z) ^((3-2y-z)+), GdO_(y)(OH)_(z) ^((3-2y-z)+),TbO_(y)(OH)_(z) ^((3-2y-z)+), DyO_(y)(OH)_(z) ^((3-2y-z)+),HoO_(y)(OH)_(z) ^((3-2y-z)+), ErO_(y)(OH)_(z) ^((3-2y-z)+),TmO_(y)(OH)_(z) ^((3-2y-z)+), YbO_(y)(OH)_(z) ^((3-2y-z)+),LuO_(y)(OH)_(z) ^((3-2y-z)+), or combinations thereof. The y and zparameters can be selected such that the ions have a positive chargebased on the particular oxidation state of the metal atom. Metalsuboxide cations of particular interest include, for example, ZrO⁺²,ZrOOH⁺, Zr(OH)₂ ⁺², Zr(OH)₃+, HfO⁺², HfOOH⁺, Hf(OH)₂ ⁺², Hf(OH)₃ ⁺combinations thereof and/or combinations with other metal suboxidecations. Furthermore, the solution can comprise additional metalcations, such as cations of copper, hafnium (Hf⁺⁴), titanium (Ti⁺⁴),zirconium (Zr⁺⁴), cerium (Ce⁺⁴), tin (Sn⁺⁴), tantalum (Ta⁺⁵), niobium(Nb⁺⁴), yttrium (Y⁺³), molybdenum (Mo⁺⁶), tungsten (W⁺⁶), aluminum(Al⁺³), gallium (Ga⁺³), zinc (Zn⁺²), chromium (Cr⁺³), iron (Fe⁺³),bismuth (Bi⁺³), scandium (Sc⁺³), vanadium (V⁺⁴), manganese (Mn⁺², Mn⁺³,Mn⁺⁴), cobalt (Co⁺², Co⁺³), nickel (Ni⁺², Ni⁺³), indium (In⁺³), antimony(Sb⁺⁵), iridium (Ir⁺³, Ir⁺⁴), platinum (Pt⁺², Pt⁺⁴), lanthanum (La⁺³),praseodymium (Pr⁺³), neodymium (Nd⁺³), promethium (Pm⁺³), samarium(Sm⁺³), europium (Eu⁺³), gadolinium (Gd⁺³), terbium (Tb⁺³), dysprosium(Dy⁺³), holmium (Ho⁺³), erbium (Eb⁺³), thulium (Tm⁺³), ytterbium (Yb⁺³),lutetium (Lu⁺³) or combinations thereof. As noted above, the state ofthe cations in solution is pH dependent, such that the initial state ofoxygen coordination can change in solution, but the trend is towardhydrolysis leading to oxide formation. It has been found thatperoxide-based ligands can hinder the formation of a metal-oxygennetwork that leads to gelation and ultimately precipitation. Thus, theperoxide can be used to form a stable state that can be quicklycondensed upon rupture of the peroxide bonds.

The metal cations generally significantly influence the absorption ofradiation. Therefore, the metal cations can be selected based on thedesired radiation and absorption cross section. It has been found thatZrO⁺² provides good absorption of ultraviolet light at 193 nm wavelengthand other far ultraviolet radiation. HfO⁺² provides good absorption ofelectron beam material and extreme UV radiation. Further tuning of thecomposition for radiation absorption can be adjusted based on theaddition of other metal ions. For example, one or more ions (cations oranions) comprising titanium, zinc, calcium, indium, tin, antimony,bismuth or combinations thereof can be added to the precursor solutionto form a coating material with an absorption edge moved to longerwavelengths, to provide, for example, sensitivity to 248 nm wavelengthultraviolet light. Also, one or more ions (cations or anions) comprisingmagnesium, boron, calcium, aluminum, silicon, phosphorous orcombinations thereof can be used to increase the absorption crosssection at shorter wavelengths. The energy absorbed is transferred tothe peroxide ligand which can result in the rupturing of the peroxidebond, which provides desired control over the material properties.

The precursor solutions can also comprise polyatomic anions, which aregenerally oxygen based. Through the formation of an ultimate inorganicoxide, oxygen-based polyatomic anions can carry over into the oxidewithin an ultimate solid material. As with the cations, the nature ofthe anions can be pH dependent. Suitable oxygen-based polyatomic anionsinclude, for example, SO₄ ⁻², BO₃ ⁻³, AsO₄ ⁻³, MoO₄ ⁻², PO₄ ⁻³, WO₄ ⁻²,SeO₄ ⁻², SiO₄ ⁻⁴, their protonated forms, and combinations thereof.Generally, the precursor solution comprises a polyatomic anionconcentration from about 0.5 to about 2.0 times the metal suboxidecation concentration, in other embodiments from about 0.75 to about 1.5times the metal suboxide cation concentration, and in furtherembodiments from about 0.8 to about 1.3 times the metal suboxide cationconcentration. A person of ordinary skill in the art will recognize thatadditional ranges of anion concentrations within the explicit rangesabove are contemplated and are within the present disclosure. Thepolyatomic anions can be added as an acid if the pH adjustment issuitable, and/or the polyatomic anions can be added along with a desiredmetal cation. The precursor solution can generally be prepared withadditional anions, such as halide anions, which may be added with themetal suboxide cations. Halide anions may react with the peroxideligands to form halogen molecules, such as Cl₂, Br₂ or I₂. The reactionwith halide ions reduces the peroxide concentrations a modest amountrelative to the added amounts of peroxide.

The peroxide-based ligands stabilize the composition with respect tocondensation. In particular, at high relative concentration ofperoxide-based ligands, significant amounts of water can be removed fromthe composition without forming a condensed metal oxide or metalhydroxide. Based on the discovery of this stabilization property,solutions can be formed with high concentrations of radiation sensitiveligands that have good shelf stability while retaining convenientprocessing to form coatings. Radiation sensitive ligands of particularinterest have a peroxide group, —O—O—. As noted above in the context ofFIG. 1, energy from absorbed radiation can break the oxygen-oxygen bond.As the peroxide groups are broken, the corresponding stabilization islost, as the composition condenses with the formation of M-O-M bonds,where M represents a metal atom. Thus, the condensation can becontrolled with radiation. Compositions with high radiation sensitiveligand concentrations can be highly stable with respect to the avoidanceof spontaneous condensation.

The chemically simplest ligand composition would be hydrogen peroxide,H₂O₂, which is soluble in water. Additional peroxide-based ligandsinclude, for example, organic compositions and/or inorganiccompositions. In some embodiments, inorganic peroxide-based ligands canbe desirable since carbon can be disadvantageous for many devices. If aninorganic peroxide is used as a radiation sensitive ligand, the risk ofcarbon contamination from the radiation sensitive ligand is avoided.Suitable inorganic peroxide ligands include, for example, peroxysulfate(SO₅H⁻), peroxydisulfate (S₂O₈ ⁻²), peroxychlorates (ClO₅H⁻), or thelike or combinations thereof. The precursor composition generallycomprises a ligand concentration of at least a factor of about 2 timesthe metal cation concentration, in further embodiments at least a factorof about 3, in other embodiments at least a factor of about 4 and inadditional embodiments a factor from about 5 to about 25 times the metalcation concentration.

In general, the desired compounds are dissolved to form an aqueoussolution. After the components of the solution are dissolved andcombined, the character of the species may change as a result ofhydration and peroxide-based ligand binding. When the composition of thesolution is referenced herein, the reference is to the components asadded to the solution since the nature of the species in solution maynot be well known.

In some embodiments, it may be desirable to form separate solutions thatcan be combined to form the precursor solution from the combination.Specifically, separate solutions can be formed comprising one or more ofthe following: the metal suboxide cations, any additional metal cations,the peroxide-based ligands and the polyatomic anions. If multiple metalcations are introduced, the multiple metal cations can be introducedinto the same solution and/or in separate solutions. Generally, theseparate solutions can be well mixed. In some embodiments, the metalcation solution is then mixed with the peroxide-based ligand solutionsuch that the peroxide-based ligand can conjugate with the metalcations. The resulting solution can be referred to as a stabilized metalcation solution. In some embodiments, the stabilized metal cationsolution is allowed to stabilize for at least about five minutes and infurther embodiments at least about 15 minutes prior to furtherprocessing. The polymeric anion solution can be added to the stabilizedmetal cation solution to form the stabilized precursor solution. Thisorder of combining the solutions can lead to more desirable results insome embodiments of the precursor solution. The solutions can becombined under appropriate mixing conditions and at appropriate rates toachieve good mixing.

The concentrations of the species in the precursor solutions can beselected to achieve desired properties of the solution. In particular,lower concentrations overall can result in a desirable properties of thesolution for certain coating approaches, such as spin coating, canachieve thinner coatings using reasonable coating parameters. Ingeneral, the concentration can be selected to be appropriate for theselected coating approach. As noted above, a relatively large ratio ofperoxide-based ligand relative to the metal cations can be used togreatly stabilize the precursor solutions. Stability of the precursorsolutions can be evaluated with respect to changes relative to theinitial solution. Specifically, a solution has lost stability if a phaseseparation occurs with the production of large sol particles. Based onthe improved stabilization approaches described herein, the solutionscan be stable for at least about 2 hours without additional mixing, infurther embodiments at least about 1 day, in other embodiments at leastabout 5 days and in additional embodiments at least about 25 days. Aperson of ordinary skill in the art will recognize that additionalranges of stabilization times are contemplated and are within thepresent disclosure. The solutions can be formulated with sufficientstabilization times that the solutions can be commercially distributedwith appropriate shelf lives.

Coating Material

A coating material is formed through the deposition of the precursorsolution onto a selected substrate. A substrate generally presents asurface onto which the coating material can be deposited, and thesubstrate may comprise a plurality of layers in which the surfacerelates to an upper most layer. The substrate surface can be treated toprepare the surface for adhesion of the coating material. Prior topreparation of the surface, the surface can be cleaned and/or smoothedas appropriate. Suitable substrate surfaces can comprise any reasonablematerial. Some substrates of particular interest include, for example,silicon wafers, silica substrates, other inorganic materials, polymersubstrates, such as organic polymers, composites thereof andcombinations thereof across a surface and/or in layers of the substrate.Wafers, such as relatively thin cylindrical structures, can beconvenient, although any reasonable shaped structure can be used.Polymer substrates or substrates with polymer layers on non-polymerstructures can be desirable for certain applications based on their lowcost and flexibility, and suitable polymers can be selected based on therelatively low processing temperatures that can be used for theprocessing of the patternable inorganic materials described herein.Suitable polymers can include, for example, polycarbonates, polyimides,polyesters, polyalkenes, copolymers thereof and mixtures thereof. Ingeneral, it is desirable for the substrate to have a flat surface,especially for high resolution applications.

Traditional organic resists are soluble in nonpolar solvents and aredeposited onto hydrophobic surfaces. The surfaces can be treated withcompounds, such as hexamethyldisilazane (HMDS), to render the surfaceshydrophobic and to promote adhesion of polymer resists. In contrast, theinorganic patternable coating materials described herein are based onaqueous solutions, which suggests that it may be desirable to apply thesolution to a hydrophilic surface for application to the substratesurface. Suitable methods can be used for particular substratecompositions to render the substrate hydrophilic, if the surface is notinitially hydrophilic to a desired degree. For silicon substrates, avariety of methods can be used to render the surface hydrophilicincluding, but not limited to, soak in a basic detergent, oxygen plasmatreatment, UV ozone treatment, soaking in a piranha etchant (3:1 mixtureof concentrated H₂SO₄(aq) and 30% by weight H₂O₂(aq)), and treating withdimethylsulfoxide (DMSO) followed by heating at about 225° C. to about275° C. for up to about 5 minutes.

In general, any suitable coating process can be used to deliver theprecursor solution to a substrate. Suitable coating approaches caninclude, for example, spin coating, spray coating, dip coating, knifeedge coating, printing approaches, such as inkjet printing and screenprinting, and the like. Some of these coating approaches form patternsof coating material during the coating process, although the resolutionavailable currently from printing or the like has a significantly lowerlevel of resolution than available from radiation based patterning asdescribed herein. The coating material can be applied in multiplecoating steps to provide greater control over the coating process. Forexample, multiple spin coatings can be performed to yield an ultimatecoating thickness desired. The heat processing described below can beapplied after each coating step or after a plurality of coating steps.

If patterning is performed using radiation, spin coating can be adesirable approach to cover the substrate relatively uniformly, althoughthere can be edge effects. In some embodiments, a wafer can be spun atrates from about 500 rpm to about 10,000 rpm, in further embodimentsfrom about 1000 rpm to about 7500 rpm and in additional embodiments fromabout 2000 rpm to about 6000 rpm. The spinning speed can be adjusted toobtain a desired coating thickness. The spin coating can be performedfor times from about 5 seconds to about 5 minutes and in furtherembodiments from about 15 seconds to about 2 minutes. An initial lowspeed spin, e.g. at 50 rpm to 250 rpm, can be used to perform an initialbulk spreading of the composition across the substrate. A back siderinse, edge beam removal step or the like can be performed with water orother suitable rinse to remove any edge bead. A person or ordinary skillin the art will recognize that additional ranges of spin coatingparameters within the explicit ranges above are contemplated and arewithin the present disclosure.

The thickness of the coating generally can be a function of theprecursor solution concentration, viscosity and the spin speed. Forother coating processes, the thickness can generally also be adjustedthrough the selection of the coating parameters. In some embodiments, itcan be desirable to use a thin coating to facilitate formation of smalland highly resolved features. In some embodiments, the coating materialscan have an average thickness of no more than about 1 micron, in furtherembodiments no more than about 250 nanometers (nm), in additionalembodiments from about 1 nanometers (nm) to about 50 nm, in otherembodiments from about 1 nm to about 40 nm and in some embodiments fromabout 1 nm to about 25 nm. A person of ordinary skill in the art willrecognize that additional ranges of thicknesses within the explicitranges above are contemplated and are within the present disclosure. Thethickness can be evaluated using non-contact methods of x-rayreflectivity and/or ellipsometry based on the optical properties of thefilm.

The coating process itself can result in the evaporation of a portion ofthe solvent since many coating processes form droplets or other forms ofthe coating material with larger surface areas and/or movement of thesolution that stimulates evaporation. The loss of solvent tends toincrease the viscosity of the coating material as the concentration ofthe species in the material increases. In general, the coating materialcan be heated prior to radiation exposure to further drive off solventand promote densification of the coating material. As a result of theheat treatment and densification of the coating material, the coatingmaterial can exhibit an increase in index of refraction and inabsorption of radiation without significant loss of contrast as a resultof thermal decomposition of the peroxide groups.

An objective during the coating process can be to remove sufficientsolvent to stabilize the coating material for further processing. Thesolvent removal process may not be quantitatively controlled withrespect to specific amounts of solvent remaining in the coatingmaterial, and empirical evaluation of the resulting coating materialproperties generally can be performed to select processing conditionsthat are effective for the patterning process. While heating is notneeded for successful application of the process, it can be desirable toheat the coated substrate to speed the processing and/or to increase thereproducibility of the process. In embodiments in which heat is appliedto remove solvent, the coating material can be heated to temperaturesfrom about 45° C. to about 150° C., in further embodiments from about50° C. to about 130° C. and in other embodiments from about 60° C. toabout 110° C. The heating for solvent removal can generally be performedfor at least about 0.1 minute, in further embodiments from about 0.5minutes to about 30 minutes and in additional embodiments from about0.75 minutes to about 10 minutes. A person of ordinary skill in the artwill recognize that additional ranges of heating temperature and timeswithin the explicit ranges above are contemplated and are within thepresent disclosure.

Patterned Exposure And Patterned Coating Material

The coating material can be finely patterned using radiation. As notedabove, the composition of the precursor solution and thereby thecorresponding coating material can be designed for sufficient absorptionof a desired form of radiation. The absorption of the radiation resultsin transfer of energy that breaks the peroxide —O—O— bonds so that atleast some of the peroxide-based ligands are no longer available tostabilize the material. With the absorption of a sufficient amount ofradiation, the exposed coating material condenses. The radiationgenerally can be delivered according to a selected pattern. Theradiation pattern is transferred to a corresponding pattern or latentimage in the coating material with irradiated areas and un-irradiatedareas. The irradiated areas comprise condensed coating material, and theun-irradiated areas comprise generally the as-formed coating material.As noted below, very sharp edges can be formed upon development of thecoating material with the removal of the un-irradiated coating material.

Radiation generally can be directed to the coated substrate through amask or a radiation beam can be controllably scanned across thesubstrate. In general, the radiation can comprise electromagneticradiation, an electron beam (beta radiation), or other suitableradiation. In general, electromagnetic radiation can have a desiredwavelength or range of wavelengths, such as visible radiation,ultraviolet radiation or x-ray radiation. The resolution achievable forthe radiation pattern is generally dependent on the radiationwavelength, and a higher resolution pattern generally can be achievedwith shorter wavelength radiation. Thus, it can be desirable to useultraviolet light, x-ray radiation or an electron beam to achieveparticularly high resolution patterns.

Following International Standard ISO 21348 (2007) incorporated herein byreference, ultraviolet light extends between wavelengths of greater thanor equal 100 nm and less than 400 nm. A krypton fluoride laser can beused as a source for 248 nm ultraviolet light. The ultraviolet range canbe subdivided in several ways under accepted Standards, such as extremeultraviolet (EUV) from greater than or equal 10 nm to less than 121 nmand far ultraviolet (FUV) from greater than or equal to 122 nm to lessthan 200 nm. A 193 nm line from an argon fluoride laser can be used as aradiation source in the FUV. EUV light has been used for lithography at13.5 nm, and this light is generated from a Xe or Sn plasma sourceexcited using high energy lasers or discharge pulses. Soft x-rays can bedefined from greater than or equal 0.1 nm to less than 10 nm.

The amount of electromagnetic radiation can be characterized by afluence or dose which is obtained by the integrated radiative flux overthe exposure time. Suitable radiation fluences can be from about 1mJ/cm² to about 150 mJ/cm², in further embodiments from about 2 mJ/cm²to about 100 mJ/cm² and in further embodiments from about 3 mJ/cm² toabout 50 mJ/cm². A person of ordinary skill in the art will recognizethat additional ranges of radiation fluences within the explicit rangesabove are contemplated and are within the present disclosure.

With electron beam lithography, the electron beam generally inducessecondary electrons which generally modify the irradiated material. Theresolution can be a function at least in part of the range of thesecondary electrons in the material in which a higher resolution isgenerally believed to result from a shorter range of the secondaryelectrons. Based on high resolution achievable with electron lithographyusing the inorganic coating materials described herein, the range of thesecondary electrons in the inorganic material is limited. Electron beamscan be characterized by the energy of the beam, and suitable energiescan range from about 5 eV to about 200 keV and in further embodimentsfrom about 7.5 eV to about 100 keV. Proximity-corrected beam doses at 30keV can range from about 0.1 microcoulombs per centimeter squared(μC/cm²) to about 5 millicoulombs per centimeter squared (mC/cm²), infurther embodiments from about 0.5 μC/cm² to about 1 mC/cm² and in otherembodiments from about 1 μC/cm² to about 100 μC/cm². A person ofordinary skill in the art can compute corresponding doses at other beamenergies based on the teachings herein and will recognize thatadditional ranges of electron beam properties within the explicit rangesabove are contemplated and are within the present disclosure.

Following exposure with radiation, the coating material is patternedwith irradiated regions and un-irradiated regions. Referring to FIGS. 2and 3, a patterned structure 100 is shown comprising a substrate 102, athin film 103 and patterned coating material 104. Patterned coatingmaterial 104 comprises condensed regions 110, 112, 114, 116 ofirradiated coating material and regions and uncondensed regions 118, 120of un-irradiated coating material. The patterned formed by condensedregions 110, 112, 114, 116 and uncondensed regions 118, 120 represent alatent image in to the coating material.

Based on the design of the inorganic coating material, there is a largecontrast of material properties between the irradiated regions that havecondensed coating material and the un-irradiated, uncondensed coatingmaterial. It has been surprisingly found that the contrast can beimproved with a post-irradiation heat treatment, although satisfactoryresults can be achieved in some embodiments without post-irradiationheat treatment.

The post-exposure heat treatment seems to anneal the irradiated coatingmaterial to improve its condensation without significantly condensingthe un-irradiated regions of coating material based on thermaldecomposition of the peroxide. For embodiments in which the heattreatment is used, the post-irradiation heat treatment can be performedat temperatures from about 45° C. to about 150° C., in additionalembodiments from about 50° C. to about 130° C. and in furtherembodiments from about 60° C. to about 110° C. The heating for solventremoval can generally be performed for at least about 0.1 minute, infurther embodiments from about 0.5 minutes to about 30 minutes and inadditional embodiments from about 0.75 minutes to about 10 minutes. Aperson of ordinary skill in the art will recognize that additionalranges of post-irradiation heating temperature and times within theexplicit ranges above are contemplated and are within the presentdisclosure. This high contrast in material properties furtherfacilitates the formation of sharp lines in the pattern followingdevelopment as described in the following section.

Development and Patterned Structure

Development of the image involves the contact of the patterned coatingmaterial including the latent image to a developer composition to removethe un-irradiated coating material. Referring to FIGS. 4 and 5, thelatent image of the structure shown in FIGS. 2 and 3 has been developedthrough contact with a developer to form patterned structure 130. Afterdevelopment of the image, substrate 102 is exposed along the top surfacethrough openings 132, 134. Openings 132, 134 are located at thepositions of uncondensed regions 118, 120, respectively.

In general, the developer can be aqueous acids or bases. Generally,aqueous bases can be used to obtain sharper images. To reducecontamination from the developer, it can be desirable to use a developerthat does not have metal atoms. Thus, quaternary ammonium hydroxidecompositions, such as tetraethylammonium hydroxide, tetrapropylammoniumhydroxide, tetrabutylammonium hydroxide or combinations thereof, aredesirable as developers. In general, the quaternary ammonium hydroxidesof particular interest can be represented with the formula R₄NOH, whereR=a methyl group, an ethyl group, a propyl group, a butyl group, orcombinations thereof. The inorganic coating materials generally can bedeveloped with the same developer commonly used presently for polymerresists, specifically tetramethyl ammonium hydroxide (TMAH). CommercialTMAH is available at 2.38 weight percent, and this concentration can beused for the processing described herein. However, in some embodimentsfor the development of the inorganic materials, the developer can bedelivered at higher concentrations relative to the concentrationsgenerally used for the development of organic resists, such as 25% byweight TMAH. Furthermore, mixed quaternary tetraalkyl-ammoniumhydroxides can be selected to provide improved line edge profiles basedon empirical evaluation. In general, the developer can comprise fromabout 2 to about 40 weight percent, in further embodiments from about 3to about 35 weight percent and in other embodiments from about 4 toabout 30 weight percent tetra-alkylammonium hydroxide. A person ofordinary skill in the art will recognize that additional ranges ofdeveloper concentrations within the explicit ranges above arecontemplated and are within the present disclosure.

In addition to the primary developer composition, the developer cancomprise additional compositions to facilitate the development process.Suitable additives include, for example, dissolved salts with cationsselected from the group consisting of ammonium, d-block metal cations(hafnium, zirconium, lanthanum, or the like), f-block metal cations(cerium, lutetium or the like), p-block metal cations (aluminum, tin, orthe like), alkali metals (lithium, sodium, potassium or the like), andcombinations thereof, and with anions selected from the group consistingof fluoride, chloride, bromide, iodide, nitrate, sulfate, phosphate,silicate, borate, peroxide, butoxide, formate,ethylenediamine-tetraacetic acid (EDTA), tungstate, molybdate, or thelike and combinations thereof. If the optional additives are present,the developer can comprise no more than about 10 weight percent additiveand in further embodiments no more than about 5 weight percent additive.A person of ordinary skill in the art will recognize that additionalranges of additive concentrations within the explicit ranges above arecontemplated and are within the present disclosure. The additives can beselected to improve contrast, sensitivity and line width roughness. Theadditives in the developer can also inhibit formation and precipitationof HfO₂/ZrO₂ particles.

With a weaker developer, e.g., lower concentration developer, a highertemperature development process can be used to increase the rate of theprocess. With a stronger developer, the temperature of the developmentprocess can be lower to reduce the rate and/or control the kinetics ofthe development. In general, the temperature of the development can beadjusted between the appropriate values of an aqueous solvent.Additionally, developer with dissolved inorganic coating material nearthe developer-coating interface can be dispersed with ultrasonicationduring development.

The developer can be applied to the patterned coating material using anyreasonable approach. For example, the developer can be sprayed onto thepatterned coating material. Also, spin coating can be used. Forautomated processing, a puddle method can be used involving the pouringof the developer onto the coating material in a stationary format. Ifdesired spin rinsing and/or drying can be used to complete thedevelopment process. Suitable rinsing solutions include, for example,ultrapure water, methyl alcohol, ethyl alcohol, propyl alcohol andcombinations thereof. After the image is developed, the coating materialis disposed on the substrate as a pattern.

After completion of the development step, the coating materials can beheat treated to further condense the material and to further dehydratethe material. This heat treatment can be particularly desirable forembodiments in which the inorganic coating material is incorporated intothe ultimate device, although it may be desirable to perform the heattreatment for some embodiments in which the inorganic coating materialis used as a resist and ultimately removed if the stabilization of thecoating material is desirable to facilitate further patterning. Inparticular, the bake of the patterned coating material can be performedunder conditions in which the patterned coating material exhibitsdesired levels of etch selectivity. In some embodiments, the patternedcoating material can be heated to a temperature from about 150° C. toabout 600° C., in further embodiments from about 175° C. to about 500°C. and in additional embodiments from about 200° C. to about 400° C. Theheating can be performed for at least about 1 minute, in otherembodiment for about 2 minutes to about 1 hour, in further embodimentsfrom about 2.5 minutes to about 25 minutes. A person of ordinary skillin the art will recognize that additional ranges of temperatures andtime for the heat treatment within the explicit ranges above arecontemplated and are within the present disclosure.

With organic resists, structures are susceptible to pattern collapse ifthe aspect ratio, height divided by width, of a structure becomes toolarge. Pattern collapse can be associated with mechanical instability ofa high aspect ratio structure such that forces, e.g., surface tension,associated with the processing steps distort the structural elements.Low aspect ratio structures are more stable with respect to potentialdistorting forces. With the patternable inorganic materials describedherein, due to the ability to process effectively the structures withthinner layers of coating material, improved patterning can beaccomplished without the need for high aspect ratio patterned coatingmaterial. Thus, very high resolution features have been formed withoutresorting to high aspect ratio features in the patterned coatingmaterial.

The resulting structures can have sharp edges with very low line-widthroughness. In particular, in addition to the ability to reduceline-width roughness, the high contrast also allows for the formation ofsmall features and spaces between features as well as the ability toform very well resolved two-dimensional patterns (e.g., sharp corners).Thus, in some embodiments, adjacent linear segments of neighboringstructures can have an average pitch of no more than about 60 nm, insome embodiments no more than about 50 nm and in further embodiments nomore than about 40 nm. Pitch can be evaluated by design and confirmedwith scanning electron microscopy (SEM), such as with a top-down image.As used herein, pitch refers to the spatial period, or thecenter-to-center distances of repeating structural elements. Featuredimensions of a pattern can also be described with respect to theaverage width of the feature, which is generally evaluated away fromcorners or the like. Also, features can refer to gaps between materialelements and/or to material elements. In some embodiments, averagewidths can be no more than about 30 nm, in further embodiments no morethan about 25 nm, and in additional embodiments no more than about 20nm. Average line-width roughness can be no more than about 2.25 nm, andin further embodiments from about 1.2 nm to about 2.0 nm. Evaluatingline-width roughness is performed by analysis of top-down SEM images toderive a 36 deviation from the mean line-width. The mean contains bothhigh-frequency and low-frequency roughness, i.e., short correlationlengths and long correlation lengths, respectively. The line-widthroughness of organic resists is characterized primarily by longcorrelation lengths, while the present inorganic coating materialsexhibit significantly shorter correlation lengths. In a pattern transferprocess, short correlation roughness can be smoothed during the etchingprocess, producing a much higher fidelity pattern. A person of ordinaryskill in the art will recognize that additional ranges of pitch, averagewidths and line-width roughness within the explicit ranges above arecontemplated and are within the present disclosure.

Further Processing of Patterned Coating Material

After forming a patterned coating material, the coating material can befurther processed to facilitate formation of the selected devices.Furthermore, further material deposition and/or patterning generally canbe performed to complete structures. The coating material may or may notultimately be removed. The quality of the patterned coating material canin any case be carried forward for the formation of improved devices,such as devices with smaller foot prints and the like.

The patterned coating material forms openings to the underlyingsubstrate, as shown for example in FIGS. 4 and 5. As with conventionalresists, the patterned coating material forms an etch mask which can beused to transfer the pattern to selectively remove an underlying thinfilm. Referring to FIG. 6, underlying thin film 103 is patterned leavingfeatures 152, 154, 156 respectively under condensed regions 110, 112,114. Compared with conventional polymer resists, the materials describedherein can provide significantly greater etch resistance.

Alternatively or additionally, the deposition of a further material canalter the properties of the underlying structure and/or provide contactto the underlying structure. The further coating material can beselected based on the desired properties of the material. In addition,ions can be selectively implanted into the underlying structure, as thedensity of the patterned inorganic coating material can provide a highimplant resistance. In some embodiments, the further deposited materialcan be a dielectric, a semiconductor, a conductor or other suitablematerial. The further deposited material can be deposited using suitableapproaches, such as solution based approaches, chemical vapor deposition(CVD), sputtering, physical vapor deposition (PVD), or other suitableapproach.

In general, a plurality of additional layers can be deposited. Inconjunction with the deposition of a plurality of layers, additionalpatterning can be performed. Any additional patterning, if performed,can be performed with additional quantities of the coating materialsdescribed herein, with polymer-based resists, with other patterningapproaches or a combination thereof.

As noted above, a layer of coating material following patterning may ormay not be removed. If the layer is not removed, the patterned coatingmaterial is incorporated into the structure. For embodiments in whichthe patterned coating material is incorporated into the structure, theproperties of the coating material can be selected to provide fordesired patterning properties as well as also for the properties of thematerial within the structure.

If it is desired to remove the patterned coating material, the coatingmaterial functions as a resist. The patterned coating material is usedto pattern a subsequently deposited material prior to the removal of theresist/coating material and/or to selectively etch the substrate throughthe spaces in the condensed coating material. The coating material canbe removed using a suitable etching process. Specifically, to remove thecondensed coating material, a dry etch can be performed, for example,with a BCl₃ plasma, Cl₂ plasma, HBr plasma, Ar plasma or plasmas withother appropriate process gases. Alternatively or additionally, a wetetch with, for example, HF(aq) or buffered HF(aq)/NH₄F can be used toremove the patterned coating material. Referring to FIG. 7, thestructure of FIG. 6 is shown after removal of the coating material.Etched structure 150 comprises substrate 102 and features 152, 154, 156.

The coating materials are particularly convenient for performingmultiple patterning using a thermal freeze process, as describedgenerally with conventional resists in P. Zimmerman, J. Photopolym. Sci.Technol., Vol. 22, No. 5, 2009, p. 625. A double patterning process witha “thermal freeze” is outlined in FIG. 8. In the first step, the coatingmaterial is formed into a pattern 160 on substrate 162 using alithographic process and development as described with respect to FIGS.4 and 5. A heating step 164 is performed to dehydrate the coatingmaterial. This heating step is equivalent to the post-developmentheating step described in the Development section above. This “thermalfreeze” process makes the coating material insoluble to a subsequentdeposition of a second layer of the coating material. A secondlithographic and development step 166 is performed to form a doublepatterned structure 168 on substrate 162. After an etch step 170, theproduct double patterned structure 172 is formed. Note that it isstraightforward to extend this process to multiple coat and patternsteps, and such extensions are contemplated and are within the presentdisclosure. With respect to multiple patterning, a significantdifference between the inorganic coating materials described herein andconventional organic resists is that organic resists remain soluble inconventional resist casting solvents even after a thermal bake. Theresist materials described herein can be dehydrated with a thermal bakesuch that they are not water soluble and subsequent coating layers canbe applied.

EXAMPLES Example 1: Preparation of Precursor Solutions

This example describes a method that has been used to prepare precursorsolutions comprising metal suboxide cations based on hafnium (Hf) and/orzirconium (Zr).

Separate aqueous solutions were prepared for the components of theprecursor solution. For convenience of notation, the respectivesolutions can be referred to as Part A for the metal suboxide cations,Part B for the peroxide-based ligand solution and Part C for thesolution comprising polyatomic anions. A solution Part A1 was preparedby filtering a solution of 0.5 mol ZrOCl₂.8H₂O (161.125, Alfa Aesar99.9%) combined with 500 mL of ultrapure water (18-MΩ·cm electricalresistance). A solution Part A2 was prepared by filtering a solution of0.5 mol HfOCl₂.8H₂O (204.76 g, Alfa Aesar 98%) combined with 500 mL ofultrapure water. As described below, Part A1 was used to form precursorsolutions for 193-nm lithography patterning, and Part A2 was used toform precursor solutions for 13-nm (also known as extreme UV or EUV) orelectron-beam lithography patterning. Solution Part B was prepared bydiluting H₂O₂(aq) (30% w/w, Mallinckrodt Baker) with ultrapure water toyield a 6-8% w/w H₂O₂(aq) solution. Solution Part C comprised 2-5 MH₂SO₄(aq) either obtained in certified concentrations (FischerScientific, 10 N) or diluted from concentrated solutions (98% H₂SO₄,Mallinckrodt Baker) with ultrapure water.

For 193-nm lithography patterning, a Zr based precursor solution wasprepared. For EUV or electron-beam lithography patterning, an Hf basedprecursor solution was prepared. The method used to prepare eitherprecursor solution was the same except that a Zr based precursorsolution was prepared with Part A1 and an Hf based precursor solutionwas prepared with Part A2. Selected ratios of component solutions PartA1 or Part A2, Part B, and Part C were measured into individualpre-cleaned polyethylene bottles. A sufficient quantity of ultrapurewater to obtain the targeted final metal concentration was added to thePart C component solution. The components in the bottles were thencombined by pouring Part A1 or Part A2 component solution into Part Bcomponent solution, waiting 5 minutes, then pouring Part C into thecombined Part A1 or Part A2 and Part B and waiting another 5 minutes.This particular mixing sequence has been found to limit particle growth.

Using the method described above, a 30 mL formulation of a Zr basedprecursor solution with a final zirconium concentration of 0.16 M wasobtained by combining 4.8 mL of solution Part A1 (Zr), 1.8 mL ofsolution Part B (H₂O₂), 2.16 mL of solution Part C (H₂SO₄(aq)), and21.24 mL of ultrapure water. Using the method described above, a 30 mLformulation of an Hf based precursor solution with a final hafniumconcentration of 0.15 M was obtained by combining 4.5 mL of solutionPart A2 (Hf), 16.875 mL of solution Part B (H₂O₂), 1.8 mL of solutionPart C (H₂SO₄(aq)), and 6.825 mL of ultrapure water.

Example 2: Preparation and Deposition of Coating Material

This example describes preparation of substrate surfaces and depositionof patternable coating materials using the precursors solutions madeaccording to Example 1.

Five inch silicon wafers were used for substrates. The surfaces of thesilicon wafers were pretreated with a basic detergent, an acidicdetergent, 02 plasma, ultraviolet ozone, piranha etch solution or DMSOwith a subsequent heating to a temperature between 225° C. and 275° C.to render the surfaces hydrophilic. The selected precursor solution wascoated on a standard lithography spin coating track. A wafer was loadedonto a spin coater, and the precursor solution was dispensed onto thecenter of the wafer. The amount of precursor solution dispensed wasselected based on the desired coating thickness and on the size of thewafer. The spin coater was spun at 100 RPM for 5 seconds to spread theresist across the wafer and then at 3000 RPM for 30-60 seconds to castthe resist film. The wafer was subjected to a pre-exposure bake at40-200° C. for 0.1-5 minutes.

This method has also been used to coat wafers with steps. FIG. 9 showscoverage of an Hf based coating material over a wafer with anapproximately 100 nm step for a thin film transistor (TFT) gatedielectric application. The coating was created from five sequentiallydeposited layers to demonstrate that step coverage is possible.Appropriate coverage on sharper steps has been observed.

Example 3: 193-Nm Lithographic Patterning of a Zr Based Coating Material

This example describes a method that has been used to pattern a Zrsuboxide based coating material.

The coating material was produced according to the method of Example 2with a ZrO⁺²-based coating composition. The coating material wasdeposited at a thickness form 10-50 nm. The Zr-based coating materialwas irradiated with patterned 193-nm (deep UV) light using alithographic processing system having an ArF laser source with a mask orgenerated interference pattern. After irradiation, the wafer was passedback to the wafer track and subjected to a post-exposure bake at 40° C.to 200° C. for 1-5 minutes. The exposure with the 193 nm UV lightresulted in a patterned coating material. The patterned coating materialwas developed with 2.38 weight percent TMAH using a puddle developmentprocess. The TMAH was contacted with the coating material for 20seconds, and then the substrate was rinsed with water and dried.Referring to FIG. 10, highly resolved patterns were produced using thedeveloper. FIG. 10 is a pattern of 120-nm pitch lines (approximately 60nm lines and spaces) in a Zr-based coating material produced by 193-nmlithography at a dose level of 20 mJ/cm².

Example 4: Electron-Beam and EUV Lithographic Patterning of an Hf BasedCoating Material

This example describes a method that has been used to pattern an Hfsuboxide based coating material.

The coating material was produced and deposited according to the methodof Example 2 with an HfO⁺² based coating composition. In one embodiment,an Hf-based coating composition was exposed with an electron-beam at 30keV and about 78 μC/cm². The resulting patterned coating material wasdeveloped with 2.38 to 25 weight percent TMAH using a dip method. Thedeveloper was contacted with the wafer for 20 seconds. Then, the waferwas rinsed with water and dried. Contact with the developer results inthe pattern as shown in FIGS. 11, 12, 13A, and 13B. Highly resolvedpatterns were produced. FIG. 11 shows 36-nm pitch lines in Hf-basedcoating material. Another pattern with a pitch of 36-nm is shown in FIG.12. This pattern was generated with an e-beam dose of 244 μC/cm².

FIGS. 13A and 13B show 36-nm pitch posts in Hf-based coating materialpatterned by electron beam radiation. The sample shown in FIG. 13A wasdeveloped with a 2.38 weight percent TMAH concentration, while thesample shown in FIG. 13B was developed with a 25 weight percent TMAHconcentration. A 25 weight percent TMAH concentration developmentresulted in more accurately defined posts, but these samples involvedabout 8×higher electron beam dose. A pattern with a 1.6 to 1.8 nm linewidth roughness is shown in FIG. 14 for a pattern with a 21 nm linewidthon a 60 nm pitch.

A double patterned structure is shown in FIGS. 15 and 16. The patterningwas performed with a 30 keV electron beam with a dose of 500 μC/cm².After the first layer was patterned, the coating was baked at 220 Cbefore the second coating was applied. A higher magnification view isshown in FIG. 16. Well resolved and uniform 30-nm contact holes arevisible in FIG. 16.

Ion etching was performed through a hard mask formed with a Hf-basedcoating material as described in this example after developing. Thecoating material functioned as a mask for the ion etching. A scanningelectron micrograph of silicon nanopillars is shown in FIG. 17. Thepatterned structure after ion etching had a pillar width of 40 nm. Themask exhibited excellent resistance to the ion etch.

The EUV images were obtained using projection lithography with anumerical aperture of 0.25 operating at 13 nm. The resist was appliedwith a thickness of 20 nm by spin coating on a silicon wafer, followedby a post-apply bake of 50° C. After exposure at approximately 80mJ/cm², a post-exposure bake of 75° C. was used prior to development in25% TMAH. The developed patterns are shown in FIGS. 18A-D. The patternsshown in FIG. 18 have pitches of A) 32-nm, B) 30-nm, C) 28-nm and D)26-nm.

The embodiments above are intended to be illustrative and not limiting.Additional embodiments are within the claims. In addition, although thepresent invention has been described with reference to particularembodiments, those skilled in the art will recognize that changes can bemade in form and detail without departing from the spirit and scope ofthe invention. Any incorporation by reference of documents above islimited such that no subject matter is incorporated that is contrary tothe explicit disclosure herein.

What we claim is:
 1. A method for forming a patterned substrate, themethod comprising: irradiating along a first pattern, a layer of a firstcoating material on the surface of the substrate having an averagethickness from about 5 nm to about 30 nm with EUV radiation at a dose ofno more than about 100 mJ/cm2; developing the patterned coating materialto remove the un-irradiated coating material; and performing an ion etchto transfer the first pattern into the substrate to form a patternedsubstrate.
 2. The method of claim 1 wherein the first coating materialprior to irradiation comprises metal ions with radiation sensitiveligands and wherein interaction of the coating material with EUV altersthe chemical properties of the first coating material creating astructure with differential dissolution rates.
 3. The method of claim 2wherein the metal of the metal ions comprises Cu, Al, Sc, Ti, V, Cr, Mn,Fe, Co, Ni, Zn, Y, Zr, Nb, Mo, In, Sn, Sb, Hf, Ta, W, Ir, Pt, La, Ce,Pr, Nb, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or a combinationthereof.
 4. The method of claim 2 wherein the metal of the metal ionscomprises Sn.
 5. The method of claim 2 wherein the first coatingmaterial prior to irradiation comprises a blend of metal ions.
 6. Themethod of claim 1 wherein the first coating material comprises anoxo/hydroxo network.
 7. The method of claim 1 wherein the substratecomprises a silicon wafer, a silica substrate, a polymer substrate,composites thereof and combinations thereof.
 8. The method of claim 1wherein the irradiation is performed with EUV at a dose of from about 1mJ/cm² to about 50 mJ/cm².
 9. The method of claim 1 wherein the firstpattern has a pitch of no more than about 40 nm.
 10. The method of claim1 wherein the developing composition comprises a reactive gas or aliquid solution.
 11. The method of claim 1 wherein the developingcomposition comprises a quaternary ammonium hydroxide.
 12. The method ofclaim 1 wherein the patterned coating material comprises a metal oxide.13. The method of claim 1 wherein the developed patterned coatingmaterial comprises openings to the substrate.
 14. The method of claim 13wherein the openings have an average width of no more than about 30 nmand/or an average line-width roughness of no more than about 2.25 nm.15. The method of claim 1 wherein the patterned substrate comprisessilicon nanopillars.
 16. The method of claim 13 further comprisingdepositing material through the openings to the substrate.
 17. Themethod of claim 1 further comprising removing the patterned coatingmaterial after performing an ion etch.
 18. The method of claim 17wherein removing the patterned coating material comprises an additionaletching process, wherein the additional etching process comprises dryetching or wet etching.
 19. The method of claim 1 further comprisingheating the substrate with the developed patterned coating material to atemperature from about 150° C. to about 600° C. for from one minute to25 minutes to form a post-patterning condensed structure.
 20. The methodof claim 19 further comprising prior to performing an ion etch:depositing a layer of a second coating material over the post-patterningcondensed structure; irradiating the second coating material over thepost-patterning condensed structure according to a second pattern; anddeveloping the second pattern to form a double patterned structure,wherein performing an ion etch comprises etching the substrate accordingto a pattern formed by the first pattern and the second pattern.